This invention relates to an insulator-type gas circuit interrupter which utilizes the inside of an insulator tube as an arc extinguishing chamber.
A general structure of a typical insulator-type gas circuit interrupter is shown in FIG. 1, and a cross section of a conventional insulator-type gas circuit interrupter disclosed in Japanese Utility Model Laid-Open No. 47-22468 for example is shown in FIG. 2. In both of the figures, the same reference numerals designate identical or corresponding components.
In FIG. 1, the typical insulator-type gas circuit interrupter comprises an insulator tube 1 having disposed therein a movable contact and a stationary contact (not shown) for opening and closing a main circuit, a support insulator 2 for supporting the insulator tube 1, and a housing 3 having disposed therein a drive mechanism (not shown because it is well known) for driving the movable contact and for fixedly supporting the support insulator 2. The insulator tube 1 is cylindrical in order that its interior can be utilized as an arc extinguishing chamber, and the top and the bottom of the cylindrical section are sealed by flanges 4 and 5. Each of the flanges 4 and 5 is provided with a terminal 6 and 7, respectively for connection to the main circuit. A drive mechanism (not shown) for driving the movable contact (not shown) is disposed within the housing 3, so that the typical structure is one where the stationary contact is disposed at the upper portion of the insulator tube 1 and the movable contact is disposed at the lower portion of the insulator tube 1.
A conventional insulator-type gas circuit interrupter as disclosed in Japanese Utility Model Laid-Open No. 47-22468 will next be described in conjunction with FIG. 2, which illustrates the interrupted state.
An insulator tube 1, which is a tapered ceramic tube for example, defines an arc extinguishing chamber 1a by closing an upper and a lower opening 1b and 1c with flanges 4 and 5. An electrically insulating gas 18 such as SF.sub.6 gas is filled within the arc extinguishing chamber 1a. A stationary contact support post 8 extends from the flange 4 downwardly along the central axis of the insulator tube 1. At the tip of the stationary contact support post 8, an arcing stationary contact 10 is disposed along the axis of the insulating tube 1 and a cluster of current carrying stationary contacts 9 is disposed to face the arcing stationary contact 10. An exhaust port 8a is formed between the arcing stationary contact 10 and the current carrying stationary contact 9 in order to discharge a flow of an insulating gas generated upon the arc extinguishing operation.
On the other hand, the flange 5 is provided thereon around the central axis of the insulator tube 1 with sliding contacts 13. A piston rod 16 is provided to oppose the stationary contact support post 8 so as to be reciprocally movable by a known drive mechanism. At the tip of the piston rod 16, an arcing movable contact 15 and a puffer cylinder 12 are provided. At the tip of the puffer cylinder 12, a current carrying movable contact 11 which is a contact material of a different metal welded to the tip is provided. At the tip of the current carrying movable contact 11, an insulating nozzle 14 is provided. Therefore, the piston rod 16, the arcing movable contact 15, the puffer cylinder 12, the current carrying movable contact 11 and the insulating nozzle 14 are physically integral with each other, so that they are reciprocatingly moved by the previously described known drive mechanism, and they are electrically connected to the flange 5 except for the insulating nozzle 14 by the puffer cylinder 12 and the piston rod 16 slide-contacting with the sliding contacts 13.
In the puffer cylinder 12, an exhaust port 12a is formed for discharging the insulating gas within the puffer cylinder 12. Also, terminals 6 and 7 are disposed on the flanges 4 and 5 for the connection to the main circuit.
In the conventional circuit interrupter, since the movable contact side must be made structurally large-sized due to a larger number of components and the provision of the puffer cylinder 12 as compared to the stationary contact side, the insulator tube 1 is arranged to have a smaller inner diameter at the stationary contact side than at the movable contact side.
The operation of the conventional circuit interrupter will now be described.
When an electric current is to be interrupted with a conventional insulator-type gas circuit interrupter of the above construction, the piston rod 16 is driven in the direction shown by an arrow X by a well-known drive mechanism from a position (closed position; not shown) in which the current carrying stationary contact 9 engages the current carrying movable contact 11, and in which the arcing stationary contact 10 engages the arcing movable contact 15. Since the current carrying stationary contact 9 and the current carrying movable contact 11 separate from each other before the arcing stationary contact 9 and the arcing movable contact 15 separate from each other, an electric arc 19 generates across the arcing stationary contact 10 and the arcing movable contact 15. As the puffer cylinder 12 moves in the arrow-X direction, the insulating gas within the puffer cylinder 12 is discharged along an arrow 18a through an exhaust port 12a to be blasted at the arc 19 generated across the arcing stationary contact 10 and the arcing movable contact 15. The insulating gas blasted at the arc 19 then flows along an arrow 18b and is discharged from an exhaust port 8a in the stationary contact support post 8 in the direction of arrows 18c and 18d. The thermal energy of the arc 19 is absorbed by the insulating gas and is expanded to be extinguished. The above arc-extinguishing principle and the arc extinguishing mechanism are well known as a puffer-type gas circuit interrupter.
The insulating gas which has been blasted at an electric arc and heated by the absorption of the thermal energy of the arc contains contact material molten upon the arc generation, so that the insulating gas is degraded in insulating property and may even have an electrical conductivity. On the other hand, in the conventional insulator-type gas circuit interrupter, since the inner diameter of the insulator tube 1 at the stationary contact side is small, the distance between the tube 1 and the stationary contact support post 8 is small, providing a problem that there is a possibility that the the stationary contact support post 8 and the insulator tube 1 are short-circuited by the high temperature, electrically conductive gas discharged from the exhaust port 8a in the stationary contact support post 8.
Also, while the heat generated during the current conduction generally tends to stay in the upper portion of the arc extinguishing chamber, the conventional insulator-type gas circuit interrupter does not have sufficient heat dissipating surface area due to the reduced diameter upper portion of the insulator tube 1, whereby the carrying current is disadvantageously limited.